The present invention relates to a liquid crystalline gel composition, a display medium, a display device and a display body using the liquid crystalline gel composition.
Various types of liquid crystal display elements have been proposed and put into practical use. A typical one is a (S)TN liquid crystal display element comprising a twisted liquid crystal molecular layer and a pair of polarizing plates for sandwiching the liquid crystal molecular layer. This type of liquid crystal display element uses polarizing plates (and a color filter in the case of a color display) and thus needs a strong backlight to provide a bright display. In view of power consumption and brightness, reflective (S)TN liquid crystal display elements and liquid crystal display elements having no polarizing plate have been proposed.
One typical display element having no polarizing plate is a polymer dispersion liquid crystal (PDLC) element. A PDLC element has a light control layer comprising a matrix of a polymer and an anisotropic liquid crystal having a positive dielectric constant and a refractive index similar to that of the polymer of the matrix and dispersed in the matrix in the form of droplets with a diameter of a few microns, and makes a display using the difference in the refractivity between the polymer matrix and the liquid crystal. When no voltage is applied, the liquid crystal molecules are not aligned. Thus, there is a difference in the refractivity between the polymer matrix and the liquid crystal droplets, and light which enters the light control layer is scattered. When a voltage is applied, the liquid crystal molecules are aligned in the direction of the voltage. Thus, the polymer matrix and the liquid crystal droplets have the substantially same refractivity, and light which enters the light control layer passes therethrough.
As another typical display element having no polarizing plate, elements having a light control layer of a liquid crystalline gel are proposed (Japanese Laid-Open Patent Publication No. H11-052341, Japanese Laid-Open Patent Publication No. H11-256164, Japanese Laid-Open Patent Publication No. 2000-239663 and Japanese Laid-Open Patent Publication No. 2000-305087). A liquid crystalline gel is a gel substance which exhibits liquid crystallinity obtained by eliminating the fluidity of a liquid crystalline compound which has fluidity by nature.
The display element disclosed in Japanese Laid-Open Patent Publication No. H11-052341 uses a compound having molecules each having at least two groups capable of intermolecular hydrogen bonding and at least two alkylene groups as a gelling agent to obtain a display element with high contrast which can be produced by a simple process as compared with conventional polymer dispersion liquid crystal elements. In the publication, a method in which a light control layer is formed by air drying a solution comprising a liquid crystal, the gelling agent and an organic solvent in a draft is shown. Certainly, the purpose of simplifying the production process is accomplished.
Japanese Laid-Open Patent Publication No. H11-256164 discloses a gel substance comprising a liquid crystalline compound and a gelling agent containing a divalent organic group having a skeleton represented by —NH—CH(—R)—CO—, and a display element using the gel substance. More specifically, a TN element comprising a pair of ITO electrodes, polyimide orientation films provided on the electrodes and subjected to rubbing treatment and a light control layer of the gel substance sandwiched between the electrodes is shown. The TN cell is excellent in responsiveness to an electric field as compared with a TN element using a non-gelled liquid crystalline compound.
According to Japanese Laid-Open Patent Publication No. 2000-239663, there is provided a display device having a light control layer of a liquid crystalline gel which exhibits a nematic, smectic or chiral smectic phase, or a ferroelectric or anti-ferroelectric liquid crystalline gel which exhibits a smectic or chiral smectic phase. The element has high stability and high shock resistance.
In Japanese Laid-Open Patent Publication No. 2000-305087, a method for applying a liquid crystalline composition containing a liquid crystalline compound and a gelling agent between a pair of substrate having subjected to orientation treatment such that the gelling agent is aligned in parallel or perpendicular to the orientation treatment direction for the purpose of improving switching properties and contrast and providing a gray scale display.
The PDLC element utilizing light scatter due to a difference in refractivity does not need a polarizing plate but has a low scattering amplitude. Thus, it cannot provide a display with high brightness and contrast. The light scattering element disclosed in Japanese Laid-Open Patent Publication No. H11-052341 is not in a satisfactory level in contrast as in the case with the PDLC element. The display element disclosed in Japanese Laid-Open Patent Publication No. H11-256164 has a low light transmissivity when no voltage is applied and thus cannot have sufficient contrast. The light scattering element and TN element disclosed in Japanese Laid-Open Patent Publication No. 2000-239663 cannot provide contrast for high visibility.
The element made by the method of Japanese Laid-Open Patent Publication No. 2000-305087 can smoothly switch the orientation of the liquid crystal molecules from horizontal to vertical but is not in a satisfactory level in contrast as in the case with the above elements.